Electronic ignition and fuel control systems for internal combustion engines are finding acceptance in the automotive and allied industries as rigid efficiency and pollution standards are imposed by the government. The first generation of these electronic controls were open loop systems which became progressively complex as the standards were raised. The number of variables needed to be detected as well as auxiliary circuits for providing corrections for these variables increased with each raising of the standards. From the conception of electronic control systems for internal combustion engines, it has been known that if the control systems could be closed about the engine, simpler control systems could be developed. This would reduce the number of variables needed to be detected, reduce the complexity of the control systems, and at the same time improve the overall efficiency. The problem that has plagued the industry is the selection of an appropriate engine parameter about which to close the loop.
K. W. Randall and J. D. Powell from Stanford University in their research under a Department of Transportation sponsored project determined that for maximum efficiency of an internal combustion engine, the spark timing should be adjusted to provide a maximum cylinder pressure at a crankshaft angle 15 degrees past the piston's top dead center position. The results of this investigation are published in a Final Report NO SUDAAR-503 entitled "Closed Loop Control of Internal Combustion Engine Efficiency and Exhaust Emission". The report contains a block diagram of a closed loop system in which a sensor detects the angle at which peak pressure occurs then compares this measured angle with the desired 15.degree. angle. An error signal, generated when the measured angle differs from the desired angle, is used to correct the ignition timing signal generated in response to the other sensed engine parameters.
Comparable closed loop ignition control systems closed about the cylinder pressure are disclosed by M. M. Peterson in U.S. Pat. No. 3,957,023 entitled "Pressure Responsive Engine Ignition System" issued May 19, 1976 and Sand in U.S. Pat. No. 3,977,373 "Closed Loop Combustion Pressure Control" issued Aug. 31, 1976.
An alternate closed loop ignition control system taught by Pratt, Jr. et al. in U.S. Pat. No. 3,897,766 entitled "Apparatus Adapted to Opto-Electrically Monitor the Output of a Prime Mover to Provide Signals which are Fed Back to the Input and Thereby Provide Control of the Prime Mover" issued Aug. 5, 1975 embodies a torque sensor which measures the twist in the output shaft of the prime mover to measure the torque. The measured torque and engine speed are used to close the loop about the engine.
Harned, et al. in U.S. Pat. No. 4,002,155 entitled "Engine and Engine Spark Timing Control with Knock Limiting, etc." issued Jan. 11, 1977 teaches a closed loop ignition system in which engine knock-induced vibrations are detected by an engine mounted accelerometer. The system counts the number of individual ringing vibrations that occur in a predetermined angular rotation of the crankshaft. When the number of ringing vibrations exceed a predetermined number, the engine spark timing is retarded and when the number of ring vibrations is less than a second predetermined number, the spark timing is advanced.
Wahl in U.S. Pat. No. 4,015,566 entitled "Electronic Ignition Control System for Internal Combustion Engines" issued Apr. 5, 1977 teaches a closed loop ignition timing system closed about an operational parameter of the engine. In his patent, Wahl teaches sensing the temperature of a catalytic converter, the exhaust gas composition (especially NO compounds), or in the alternative using vibration sensor to detect a rough running engine. The use of engine roughness as the measured parameter is similar to the system taught by Harned in U.S. Pat. No. 4,002,155 discussed above. In still another type of closed loop system, Schweitzer, et al. in U.S. Pat. No. 4,026,251 entitled "Adaptive Control System for Power Producing Machines" issued May 31, 1977 teaches dithering the ignition timing and closing the loop about the engine's speed.
The closed loop ignition timing systems in which the cylinder pressure is measured directly as taught by Randall and Powell and implemented in the patents to Peterson and Sand appear as the most direct and effective engine parameter about which to close the loop. However, this method requires a pressure transducer to be incorporated into at least one of the engine's cylinders where it is exposed to high temperatures and high pressures. Such pressure sensors are costly, have relatively short life expectancies and require additional modification to the engine for their use. Alternatively, pressure sensors adapted to be used in conjunction with the spark plugs are known but still suffer from the first listed deficiencies. The direct measurement of engine torque as taught by Pratt, Jr., et al. is an alternative approach but requires a relatively complex and expensive torque measuring sensor. The measurement of the onset of engine work or roughness as taught by Harned, et al. and Wahl respectively are believed to be too inaccurate to meet today's standards while the system taught by Schweitzer is believed to be ineffective because factors other than ignition timing such as a change in load could affect the engine speed and result in improper ignition timing.
Various types of closed loop fuel control systems for internal combustion engines have been developed in which the loop is closed about the different engine parameters. The one of the parameters about which the loop is closed is the composition of the exhaust gas as taught by Seitz in U.S. Pat. No. 3,815,561 "Closed Loop Engine Control System" issued June 11, 1974 as well as many others. The system taught by Seitz uses an oxygen (O.sub.2) sensor detecting the concentration of oxygen in the exhaust gas and closes the loop about a stoichiometric mixture of air and fuel. However, a stoichiometric mixture of air and fuel has been found to be too rich for the efficient operation of the engine. Various techniques have been employed to operate the engine at leaner air fuel ratios but the ability to achieve reliable closed loop control at the desired leaner mixture is limited by the characteristics of the present day oxygen sensors.
An alternate approach is taught by Taplin, et al. in U.S. Pat. No. 3,789,816 "Lean Limit Internal Combustion Engine Roughness Control System" issued Feb. 5, 1974 in which engine roughness is detected as the parameter about which the loop is closed. In this system, the air/fuel mixture is leaned out until a predetermined level of engine roughness is achieved. The magnitude of engine roughness is selected to correspond with a level of engine roughness at which the air fuel mixture is made as lean as possible to the point that the formation of such exhaust gas as HC and CO is minimized without the driveability of the particular vehicle being unacceptable. Engine roughness as measured in the Taplin, et al. patent is the incremental change in the rotational velocity of the engine's output as a result of the individual torque impulses received from each of the engine's cylinders. The closing of the fuel control loop about engine roughness appears to be the most effective means for maximizing the fuel efficiency of the engine.
Leshner, et al. in U.S. Pat. No. 4,015,572 teaches a similar type of fuel control system in which the loop is closed about engine power. In their preferred embodiment, Leshner, et al. use exhaust back pressure as a manifestation of engine power, however, state that a measured torque, cylinder pressure, of a time integral of overall combustion pressure for one or more engine revolutions at a given RPM may be used in the alternative. In a more recent advertising brochure "Breaking the Lean Limit Barrier", Fuel Injection Development Corporation of Bellmawr, N.J., the assignee of the Leshner, et al. patent states that the parameter measured is the velocity of the engine's flywheel.
In another type of fuel control system using engine roughness as the sensed parameter to close the loop, Bianchi, et al. in U.S. Pat. No. 4,044,236 teaches measuring the rotational periods of the crankshaft between two sequential revolutions of the engine. The differential is digitally measured in an up-down counter counting at a frequency proportional to the engine speed.
In an alternate type of roughness closed loop fuel control system, Frobenius, et al. in U.S. Pat. No. 4,044,234 "Process and Apparatus for Controlling Engine Operation Near the Lean-Running Limit" issued August, 1977 teaches measuring the rotational period of two equal angular intervals, one before and one after the top dead center position of each piston. The change in the difference between the two rotational periods for the same cylinder is compared against a particular reference value and an error signal is generated when the change exceeds the reference value. Frobenius in U.S. Pat. No. 4,044,235 "Method and Apparatus For Determining Smooth Running Operation in an Internal Combustion Engine" issued August, 1977 teaches an alternate roughness control system wherein the periods of three sequential revolutions are compared to determine engine smoothness. The above reflects various ways in which engine roughness as detected by various means including the variations in the rotational velocity of the flywheel is used to close the loop about the engine.
The prior art teaches independent closed loop control systems, in which each control, i.e., ignition timing, fuel control, and fuel distribution are treated as separate entities. The applicants herein teach an integrated engine control system in which the control loops for each controlled parameter is closed about a single measured engine operating parameter and in particular, the instantaneous rotational velocity of the engine's crankshaft. The data obtained from the singularly measured parameter is processed in different ways to generate timing and fuel delivery correction signals optimizing the conversion of combustion energy to rotational torque by the engine.